The polyphenylene ethers and processes for their preparation are well known in the art. They are described in Hay, U.S. Pat. No. 3,306,874 and U.S. Pat. No. 3,306,875 and Blanchard et al, U.S. Pat. No. 3,219,625 and U.S. Pat. No. 3,219,626 all of which are incorporated by reference. Other patents which show the preparation of polyphenylene ethers include Price et at, U.S. Pat. No. 3,382,212; Kobayashi et al, U.S. Pat. No. 3,455,880; Bennett and Cooper, U.S. Pat. No. 3,796,698; Bennett and Katchman, U.S. Pat. No. 3,787,362; Cooper, U.S. Pat. No. 3,733,307; Cooper and Bennett, U.S. Pat. No. 3,733,299, all of which are incorporated by reference.
The processes most generally used to produce the polyphenylene ethers involve the self-condensation of a monovalent phenol in the presence of an oxygen-containing gas and a catalyst comprising a metal-amine complex.
These processes are carried out in the presence of an organic solvent and the reaction is usually terminated by removal of the catalyst from the reaction mixture. This has been carried out by extraction with mineral acids such as hydrochloric or sulfuric acid.
Extraction with organic acids such as acetic acid has also been used. This procedure also gives good copper removal and extracts both copper and amine into the aqueous phase. A separate step (neutralization and distillation) is required to recover the amine; this is also true for extraction with mineral acid. Also, bisulfates, ammonium salts and chelating agents such as EDTA, triethylene tetraamine, etc., have been employed for this purpose.
Aqueous extraction has been carried out in such a manner that the aqueous extracting fluid has been dispersed throughout the organic phase which comprises the polyphenylene ether, the reaction solvent and the copper amine catalyst. Because of the very fine dispersion of the aqueous phase in a high viscosity organic phase and because of the inter-phase surface tension of the dispersed aqueous extractant, the different phases do not readily phase separate on standing; and a portion of the aqueous phase remains within the organic phase. Thereafter, when an antisolvent is added to the mixture, the polyphenylene ether precipitates and the catalyst residue is taken up by the antisolvent. When the antisolvent is passed through a recovery system, the catalyst residue is difficult to separate and causes the equipment to become fouled. This problem makes it desirable to remove the catalyst residue from the antisolvent prior to passing it through the recovery system. This can be done using absorbents and evaporative techniques but these procedures are quite costly.
It has now been found that the problem of catalyst residues in the antisolvent may be overcome by varying the conventional liquid-liquid extraction process so that a continuous aqueous phase is always maintained while a discrete organic phase is maintained. The result of this process is the substantially complete removal of the copper-amine catalyst residue from the polyphenylene ether reaction solution so that the copper-amine catalyst is not carried into the antisolvent that is used to separate the polyphenylene ether resin from its reaction solvent.
Accordingly, it is a primary object of this invention to provide an improved liquid-liquid extraction process for the separation of a copper-amine catalyst from a polyphenylene ether reaction mixture which does not result in the entrapment of the aqueous extracting liquid in the organic phase which contains the polyphenylene ether.
It is also an object of this invention to provide a rapid method of separating a copper-amine catalyst from a polyphenylene ether reaction mixture.